We identified a 6-aminoquinolone compound, WC5, that inhibits human cytomegalovirus (HCMV) replication with a selectivity index of approximately 500. WC5 also showed activity against drug-resistant HCMV strains. In contrast, it did not significantly affect the replication of human herpesvirus 6 and 8 and was approximately 10-fold less active against murine cytomegalovirus. Thus, WC5 may represent a lead for the development of new, potent, and selective anti-HCMV compounds.